Control of the biodegradation rates of biologically compatible microstructures to selectively control the biodegradation rates of three-dimensional biological scaffolds, such as ordered open-cellular polymer structures, is desirable when such are used as biological growth templates.
Manufactured medical devices that are implanted in a human body have been widely used for years in medicine. The applications of implantable medical devices are numerous, including orthopedic, vascular and biomedical research.
In clinical medicine, conventional use of metals, for example, steel and titanium, are common as implantable medical devices due to their mechanical strength. Typically, in surgeries that require fixing fractures, these implantable medical devices can be used to address bone fractures by attaching a reinforcing rod or a plate to a fractured bone so that the broken ends may be stabilized to promote fusion and consequent healing. Particularly in the sports medicine area, medical devices are used to repair and augment soft tissues, such as anterior cruciate ligament (ACL) replacement. Further, implantable medical devices such as screws are used to affix bone fragments to bone structure of a patient.
A disadvantage associated with these metal implantable medical devices, however, is that they are often not biocompatible in the body, and are not biodegradable. Problems associated with these metal medical devices can include inflammation at the wound healing site, adverse affects on the surrounding tissue and, additional surgeries might be required to remove these implants from the body since they are not degradable which can be both costly and traumatic for the patient.
Recently, there has been interest in using biomaterials for the use as bioabsorbable materials in medical implants. Bioabsorbable materials can be used therapeutically, prophylactically, diagnostically and can be beneficial in the medical field.
Though metals have long been used as implantable medical devices, biodegradable materials, materials that degrade in the body, and then are absorbed into the body, have been used as an alternative to metals. Specifically designed biodegradable materials can have mechanical properties that begin to approach those of bone in some applications.
As healing progresses, the stiffness and strength of the biodegradable material implant gradually decrease, transferring loads from the implant to the healing bone tissue. Recently, synthetic polymers have been used as biodegradable materials in an implantable medical device. Such polymers include, for example, poly(glycolide), poly(lactide), I-polyactic-polyglycolic acids (PLGA) and I-polyactic acids (I-PLA). Often, however, these polymers, can be slow to degrade, often taking over one year to be absorbed by the body. Several of these polymers have been used as medical device and have controlled degradation rates. These controlled degradation rates, however, typically are based on the chemistry of their original polymer structure, often decreasing their mechanical strength in vivo and possibly altering their backbone structure. Additionally, once these polymers are implanted in the body, there is often no control on the rate of degradation.
Currently, there has been interest in scaffold-based biological tissue engineering requiring the formation of new tissues, which is strongly dependent on the three-dimensional environment provided by the scaffold. Characteristics of the scaffold that can influence the three-dimensional environment include its composition, its porous architecture, and its biological response to surrounding tissues/cellular media.
Despite the availability of these biodegradable synthetic polymers, there is a need to develop biodegradable polymers, which can further extend the range of available properties, yet perform their function in vivo while maintaining their mechanical properties while being degraded. It would be desirable to have biodegradable polymers that one skilled in the art could selectively control the rate of degradation. It would be ideal to have polymer with selective degradation rates of less than one year. In addition, it would be desirable to have a three dimensional biological polymer scaffold, with a micro-truss type cellular architecture than can be tuned to have specific mechanical properties and degradation times. Such three-dimensional biological scaffolds that can enable specific/tissue cell growth can be well suited for use as a medical implant device that could degrade over a predetermined period of time.